Several of the Junto members worked closely with him. At first they electrified the tube, as was still done in Europe, by vigorously rubbing one side of it with a piece of buckskin. One of the club members, a Silversmith named Philip Synge, devised a sort of grindstone, which revolved the tube as one turned a handle. To charge the tube with electricity, all that was needed was to hold the buckskin against the glass as it revolved, a vast saving in physical labor.
Another invention of Franklin and his associates was the first storage battery. For electrical plates they used eleven window glass panes about six by eight inches in size, covered with sheets of lead, and hung on silk cords by means of hooks of lead wire. They found it as easy to charge this “battery” with frictional electricity as to charge a single pane of glass.
Among his disciples was an unemployed Baptist minister named Ebenezer Kinnersley. Franklin suggested he might both serve science and earn his living if he held electrical demonstrations. Kinnersley’s first announcement of a lecture, held in Newport, described “electrical fire” as having “an appearance like fishes swimming in the air,” claiming this fire would “live in water, a river not being sufficient to quench the smallest spark of it.” He promised his audience such wonders as “electrified money, which scarce anybody will take when offered ... a curious machine acting by means of electric fire, and playing a variety of tunes on eight musical bells ... the force of the electric spark, making a fair hole through a quire of paper....”
Kinnersley lectured in the colonies and the West Indies and was hugely successful. Neither he nor any of the other collaborators could rival Franklin’s own achievements.
Early in 1747, he gave the names of positive and negative (or plus and minus) to the two types of electricity, to replace the unwieldy terms, resinous and vitreous. Positive and negative electricity became part of the scientific vocabulary. He was the first to refer to the conductivity of certain substances. Electricity passed easily through metals and water; they were conductive. Glass and wood were nonconductive, unless they were wet. He also noted that pointed metal rods were wonderfully effective “in drawing off and throwing off the electrical fire.”
After he retired in 1748, he spent much more time on electricity. To Peter Collinson in London he wrote, “I never was before engaged in any study that so totally engrossed my attention and my time as this has lately done.” He kept Collinson informed in detail of his experiments, not because he thought he had the final word but in the hope that his experiments might possibly prove helpful to English scientists.
It was to Collinson he described an electrical party to be held on the banks of the Schuylkill River in the spring of 1749: “A turkey is to be killed for our dinner by the electrical shock, and roasted by the electrical jack, before a fire kindled by the electrified bottle; when the healths of all the famous electricians in England, Holland, France, and Germany are to be drank in electrified bumpers, under the discharge of guns from an electrical battery.”
For Christmas dinner that year, he started to electrocute another turkey, but inadvertently gave himself the shock intended for the fowl: “The company present ... say that the flash was very great and the crack as loud as a pistol.... I neither saw the one nor heard the other.... I then felt ... a universal blow throughout my whole body from head to foot.... That part of my hand and fingers which held the chain was left white, as though the blood had been driven out, and remained so eight or ten minutes after, feeling like dead flesh; and I had a numbness in my arms and the back of my neck which continued till the next morning but wore off.”
He was apologetic rather than frightened by the near catastrophe, comparing himself to the Irishman “who, being about to steal powder, made a hole in the cask with a hot iron.”
This was soon after he had come to the conclusion that what he now called “electrical fluid” had much in common with lightning—that indeed they might be one and the same thing. He was not the first to propose this theory but no one before him had been able to suggest how it might be tested.